COMMON ELECTROANALYTICAL BEHAVIOR OF LI INTERCALATION PROCESSES INTO GRAPHITE AND TRANSITION-METAL OXIDES

This paper compares the electroanalytical behavior of lithiated graphi te. LixCoO2, LixNiO2, and LixMn2O4 spinel electrodes. Slow scan rate c yclic voltammetry (SSCV), potentiostatic intermittent titration (PITT) , and electrochemical impedance spectroscopy (EIS) were applied in ord er to study the potentiodynamic behavior, the variation of the solid-s tate diffusion coefficient, and the impedance of these electrodes. In addition, X-ray diffractometry and Fourier trans form infrared (FTIR) spectroscopy were used in order to follow structural and surface chemi cal changes of these electrodes upon cycling. It was found that all fo ur types of electrodes behave very similarly. Their SSCV are character ized by narrow peaks which may reflect phase transition between interc alation stages, and the potential-dependent Li chemical diffusion coef ficient is a function with sharp minima in the vicinity of the CV peak potentials, in which the differential electrode capacity is maximal. The impedance spectra of these electrodes reflect an overall process o f various steps in series. These include Li+ ion migration through sur face films, charge transfer which depends strongly on the potential, s olid-state diffusion and, finally, accumulation of the intercalants in their sites in the bulk of the active mass, which appears as a strong ly potential-dependent, low-frequency capacitive element. It is demons trated that the above electroanalytical response, which can be conside red as the electrochemical fingerprint of these electrodes, may serve as a good in situ tool for the study of capacity fading mechanisms.